Constant energy source



Jan. 16, 1962 R. w. FRITTS CONSTANT ENERGY SOURCE Original Filed Oct.30, 1957 A i 42 71111711111110 l INVENTOR. ROBERT W. FR ITTS ATTORNEYSUnited States Patent Ofiice 3,017,444 Patented Jan. 16, 1962 3,017,444CONSTANT ENERGY SDURCE Robert W. Fritts, Arden Hills, Minn., assignor,by mesne assignments, to Minnesota Mining and Manufacturing Company, St.Paul, Minn, a corporation of Delaware Original application Oct. 30,1957, Ser. No. 693,363, new Patent No. 2,952,724, dated Sept. 13, 1960.Divided and this application June 27, 1960, Ser. No. 39,065

4 Claims. (Cl. 136--4) This invention relates to constant energysources, and more particularly to sources in which a constant electricalpotential is available from a thermoelectric generator, and thisapplication is a division of my application Serial No. 693,308, filedOctober 30, 1957, now Patent No. 2,952,724.

In order for a thermoelectric generator to provide a source of constantelectrical energy, it is necessary that a fixed temperature differentialbe maintained between the hot and cold thermojunctions thereof. This, ofcourse, can be accomplished by maintaining the hot and coldthermojunctions at predetermined fixed temperatures, but heretofore nosatisfactory means has been available for maintaining such fixedtemperatures. Common temperature controlling means operate on theprinciple of correcting for any departure from the predeterminedtemperature and for this reason cannot maintain a constant temperature.In certain applications the maintenance of a predetermined temperaturelevel depends upon continuous energization of the temperaturecontrolling means at a constant value, and any variation in theenergizing current, however small, results in departure of thetemperature from the desired level.

With the above in mind, it is a general object of the present inventionto provide apparatus affording a constant energy source and havingembodied therein a thermoelectric generator and electroresponsive meansfor maintaining the thermojunctions of said generator at a constanttemperature differential despite slight variations in the energizingcurrent supplied to said electroresponsive means.

Another object of the invention is to provide apparatus of theaforementioned character wherein the means for maintaining thethermojunctions of the generator at a constant temperature differentialcomprises two constant temperature baths or media with which saidthermojunctions are thermally associated and which undergo a change ofphysical state at predetermined temperatures at which it is desired tomaintain the associated generator thermojunctions, said means alsoincluding heat transfer means operable when energized to maintain aportion of each of said media in one physical state, for example solid,and the remainder in the other physical state, for example liquid, suchthat said media and hence said thermojunctions are maintained constantat the transformation temperature of said media.

Still another object of the invention is to provide apparatus of theclass described wherein both media are of such a character that thetransformation temperatures thereof are above ambient but aresubstantially disparate, there being a single heat supplying meansoperatively associated with both of said media to effect liqueficationof a portion of each of said media.

Another object of the invention is to provide apparatus as aforestatedwherein the heat transfer means includes a thermoelectric heat pumphaving semi-metallic thermoelements.

Other objects and advantages of the invention will become apparent asthe description proceeds, reference being had to the accompanyingdrawing illustrating the invention and wherein:

The FIGURE is a vertical sectional view of one form of apparatusconstructed in accordance with the principles of the present invention.

The embodiment of the invention shown in the drawing comprises acontainer 10 having a cup-shaped lower member 12 formed of material oflow thermal conductivity, such as rubber or synthetic resins, and asleeve member 14 formed of material of relatively high thermalconductivity, for example metal, sealingly threaded into said basemember and provided with cooling fins 93. An inverted cup-shapedcontainer portion 16 is sealingly threaded onto sleeve member 14, and apartition wall 18 formed of material of low electrical and thermalconductivity divides the interior of container 10 into chambers 24 and25, there being means such as brackets 2d and screws 22 which retainsaid partition wall in the operative position shown.

Embedded within partition wall 18 is a thermoelectric generator 27comprising P and N type thermoelements 28 and 30 respectively,thermojunction member 32, and thermojunction and terminal members 34 and36. Thermoelements 28 and '30 may, for example be made of thesemi-metallic compositions disclosed in US. Patent No. 2,811,570 orPatent No. 2,811,571. Lead wires 33 and 40 are connected to the members34 and 36 respectively, and a heating coil surrounds an extended portion18a of the partition 18 adjacent the thermojunction member 32 and isconnected to a source of alternating current (not shown) by means oflead wires 82 and 84.

Disposed in the upper end of the chamber 24 is a heat conducting plate9% of material, such as metal, having good thermal conductivity. Theplate is supported by a heat conducting rod 91 integral therewith andextending downwardly therefrom through the thermojunction member 32 andpartition 18, terminating in the lower portion of the chamber 26. Therod '91 is also of material of good thermal conductivity. The partition18 has a tubular extension 92 extending through a suitable opening inthermojunction member 32 and surrounding and insulating the portion ofthe rod 91 Within the chamber 24.

Within chamber 24 is a fill 42 in intimate contact with heating coil80', thermojunction member 32 of generator 27, and heat conducting plate90. Within chamber 26 is a fill 44 in intimate contact withthermojunction and terminal members. 34 and 36 and with the lower endportion of the heat conducting rod 91. Fill 42 is transformable from oneto another physical phase or state, for example from solid to liquid, ata temperature somewhat above the temperature of the ambient atmosphere.A relatively high melting point paraffin is an example of one materialwhich meets the above requirement. The fill 44 is also transformablefrom one to another physical phase or state, for example from solid toliquid, at a temperature somewhat above ambient temperature, whichtransformation temperature is preferably substantially below thetransformation temperature of the fill 42. A relatively low meltingpoint paraflin is an example of a material which is satisfactory for useas the fill 42.

The embodiment of the invention shown in the drawing operates asfollows:

Energization of the heater coil 80 supplies heat to the fill 42 raisingthe temperature thereof above ambient. A portion of the heat supplied tothe fill 42 flows by conduction through plate 90 and rod 91 to the fill44, and a minor portion of said heat may flow to the fill 44 byconduction through the thermoelements 28 and 30. A certain amount ofheat may also be lost from the fill 4'2 by conduction through thecontainer member 12.

The heater coil 80 and the energizing current supplied thereto throughthe conductors 82 and 34 are of such a character that continuous currentflow through said coil maintains a portion of the fill 42 transformed tothe liquid phase, while the remainder thereof stays in the solid phasein which it normally occurs at ambient temperature. A state ofequilibrium is eventually reached wherein the amount of heat deliveredto fill 42 by continuous current fiow through heating coil 80, is equalto the amount of heat lost from fill 42 to the fill 44 and to theambient atmosphere. This thermal equilibrium preferably occurs in fill42 when approximately one-half of said fill is in the liquid phase orstate and the remainder is in the solid state or phase.

Since heat conducting plate 96 and rod 91 afford the principal means fortransferring heat from fill 42 to fill 44, and sleeve 14 with its fins93 affords means for conducting heat from fill 44 to the surroundingenvironment, proper selection of the material used as fill or medium 44results in the utilization of the heat fiow from fill 42 into fill 44 tomaintain fill 44 at its transformation temperature. By proper selectionof the structural elements and of fill 44 the heat How to the fill 44from fill 42 can be made substantially equal to that lost from fill 44to the atmosphere, and a state of thermal equilibrium is reached whereinapproximately one-half of said fill is transformed to the liquid phaseor state while the remainder thereof stays in the solid state in whichit normally occurs at ambient temperature.

Thus, by continuous current flow through heating coil 80, the heatcontent of each of fills 42 and 44 is so stabilized that each of saidfills is approximately fifty percent in each of two physical states orphases. Under these conditions, if the energizing current supplied tothe heating coil 8% should vary so as to vary the quantity of heat perunit time delivered from said coil to fill 42, or the environmentaltemperature should change to vary the quantity of heat transferred tothe environment, the ratio of the two physical states or phases of eachof the fills 42 and 44 varies accordingly until a new state ofequilibrium is reached. Because advantage is taken of the latent heat oftransformation of the fills 42 and 44, such variation in theenergization of coil 80 and/or in environmental temperature does not inany way vary the temperatures of said fills which remain constant attheir respective transformation temperatures.

By virtue of the intimate contact between thermojunction member 32 andfill 42 thermojunctions thereat are also maintained at thetransformation temperature of said fill. In like manner, the intimatecontact of the thermojunction and terminal members 34 and 36 with fill44 insures that the thermojunctions thereat are maintained at thetransformation temperature of fill 44. Thus, the thermojunctions at theopposite ends of the thermoelements 28 and 30 are maintained constant atpredetermined specific and substantially different temperatures, andthis, of course, causes generator 27 to provide a constant electricaloutput potential at the conductors 38 and 40 in the manner of a standardcell.

Although a specific embodiment of the invention has been shown anddescribed, it is with full awareness that many changes and modificationstherein are possible with out departing from the spirit of theinvention. All of such changes are contemplated as may come within thescope of the appended claims.

What is claimed as the invention is:

1. Constant output energy source means comprising, a thermoelectricgenerator having at least two thermojunctions, a bath comprising a firstmedium transformable from a solid state to a liquid state at a firstpredetermined temperature above a predetermined range of ambient roomtemperatures external to said bath, said medium being in thermal contactwith one of said thermojunctions, a bath comprising a second mediumtransformable from a solid state to a liquid state at a second lowerpredetermined temperature above said range of ambient temperatures andin thermal contact with another of said thermojunctions, electricallyenergizable means having a heat emitting portion in said first bath andsupplying heat to said first medium in quantity sufiicient to maintain aportion only of said first medium in a liquid state, means communicatingbetween said baths and having surface portions in thermal contact withboth of said media for conducting heat from said first to said secondmedium to cause solid phase portions of said first medium to tend tocollect on the surface portion of said conducting means in contacttherewith as a result of extraction of heat from said first mediumthrough said surface portion, and heat transfer means having a heatabsorbing portion in thermal contact with said second medium fortransferring heat to the ambient atmosphere from said second medium insuflicient quantity to maintain a portion only of said second medium inits solid phase and deposited on said heat absorbing portion, therebycontrolling the heat content of both of said media in a manner to causeeach of said media to have portions in both liquid and solid phases tomaintain the temperatures of said media and hence those of theassociated thermojunctions constant at the transformation temperaturesof said media, the constant temperature differential between said oneand another thermojunction thus produced aifording said generatorconstant output potential.

2. Constant output energy source means comprising, a thermoelectricgenerator having at least two thermojunctions, a bath comprising a firstmedium transformable from a solid state to a liquid state at a firstpredetermined temperature above a predetermined range of ambient roomtemperatures external to said bath, said medium being thermallyassociated with one of said thermojunctions, a bath comprising a secondmedium transformable from a solid state to a liquid state at a secondlower predetermined temperature above said range of ambient temperaturesand thermally associated with another of said thermojunctions,electrical resistance heating means in said first bath and supplyingheat to said first medium in quantity sufficient to maintain a portiononly of said first medium in a liquid state, heat conducting meanscommunicating between said baths and having surfaces in thermal contactwith both of said media for conducting heat from said first to saidsecond medium to cause solid phase portions of said first medium to tendto collect on the surface of said conducting means in contact therewithas a result of extraction of heat from said first medium through saidsurface, and heat transfer means in thermal contact with said secondmedium and having heat dissipating surfaces exposed to the ambientatmosphere for transferring heat to the ambient atmosphere from saidsecond medium in sutficient quantity to maintain a portion only of saidsecond medium in its solid phase and deposited on said heat transfermeans, thereby controlling the heat content of both of said media in amanner to cause each of said media to have portions in both liquid andsolid phases to maintain the temperatures of said media and hence thoseof the associated thermojunctions constant at the transformationtemperatures of said media, the constant temperature differentialbetween said one and another thermojunction thus produced affording saidgenerator constant output potential.

3. Constant output energy source means comprising, means defining aninsulating container, partition means separating the interior of saidcontainer into two chamhers, a thermoelectric generator extendingthrough said partition means and having at least one thermojunction ineach of said chambers, a first medium in one of said chamberstransformable from a solid state to a liquid state at a firstpredetermined temperature above a predetermined range of ambient roomtemperatures external to said bath, said medium being thermallyassociated with said thermojunction in said one chamber, a second mediumin the other of said chambers transformable from a solid state to aliquid. state at a second lower predetermined temperature above said.range of ambient temperatures and thermally associated with. saidthermojunction in said other chamber, electrically energizable heatingmeans in said first chamber for supplying heat to said first medium inquantity suflicient to maintain a portion only thereof in a liquidstate, heat conducting means extending through said partition means andhaving a surface in said one chamber in contact with said first mediumand a surface in said other chamber in contact with second medium forconducting heat from said first to said second medium, and heat transfermeans extending through said container wall and having a heat absorbingportion in said other chamber in thermal contact with said second mediumfor transferring heat to the ambient atmosphere from said second mediumin sulficient quantity to maintain a portion only of said second mediumin its solid phase, thereby controlling the heat content of both of saidmedia in a manner to cause each of said media to have portions in bothliquid and solid phases to maintain the temperatures of said media andhence those of the associated thermojunctions constant at thetransformation temperatures of said media, the constant temperaturedifferential between said one and another thermojunction thus producedaffording said generator constant output potential.

4. A constant output energy source means comprising, means defining aninsulating container, partition means separating the interior of saidcontainer into two chambers, a thermoelectric generator extendingthrough said partition means and having at least one thermojunction ineach of said chambers, a first medium in one of said chamberstransformable from a solid state to a liquid state at a firstpredetermined temperature above a predetermined range of ambient roomtemperatures external to said bath, said medium being thermallyassociated with said thermojunction in said one chamber, a second mediumin the other of said chambers transformable from a solid state to aliquid state at a second lower predetermined temperature above saidrange of ambient temperatures and thermally associated with saidthermojunction in said other chamber, electrical resistance heatingmeans in said first chamber for supplying heat to said first medium inquantity sufficient to maintain a portion only thereof in a liquidstate, heat conducting means extending through said partition means andhaving a surface in said one chamber in contact with said first mediumand a surface in said other chamber in contact with said second mediumfor conducting heat from said first to said second medium, and heattransfer means extending through said container Wall and having a heatabsorbing portion in said other chamber in thermal contact with saidsecond medium and heat dissipating means external to said container fortransferring heat to the ambient atmosphere from said second medium insufiicient quantity to maintain a portion only of said second medium inits solid phase, thereby controlling the heat content of both of saidmedia in a manner to cause each of said media to have portions in bothliquid and solid phases to maintain the temperatures of said media andhence those of the associated thermojunctions constant at thetransformation temperatures of said media, the constant temperaturediiferential between said one and another thermojunction thus producedaffording said generator constant output potential.

References Cited in the file of this patent UNITED STATES PATENTS

